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When logging in to a Matrix account, Thunderbird used the homeserver address provided in the server's login response without validating it.

CVE-2026-118180

When logging in to a Matrix account, Thunderbird used the homeserver address provided in the server's login response without validating it. A malicious or compromised homeserver could provide a file: URL, causing Thunderbird to send all further Matrix requests of that session to local files or, on Windows, to an attacker-controlled network share, which could leak the user's NTLM credentials. The NTLM credential leak only affects Thunderbird on Windows. Other operating systems are unaffected. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

Assessment

CVSS
Not yet scored
Severity
Unscored
Known exploited
Not listed in CISA KEV
Exploit availability
Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published
27 October 2026
Last updated
28 October 2026
Assigner
security@mozilla.org

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